蔣仲安,鄧權(quán)龍,時(shí)訓(xùn)先,陳舉師
(1.北京科技大學(xué) 金屬礦山高效開(kāi)采與安全教育部重點(diǎn)實(shí)驗(yàn)室,北京 100083; 2.中國(guó)安全生產(chǎn)科學(xué)研究院 工業(yè)安全研究所,北京 100012)
石棉篩分車(chē)間粉塵質(zhì)量濃度分布規(guī)律的數(shù)值模擬*
蔣仲安1?,鄧權(quán)龍1,時(shí)訓(xùn)先2,陳舉師1
(1.北京科技大學(xué) 金屬礦山高效開(kāi)采與安全教育部重點(diǎn)實(shí)驗(yàn)室,北京 100083; 2.中國(guó)安全生產(chǎn)科學(xué)研究院 工業(yè)安全研究所,北京 100012)
為了掌握石棉選礦廠篩分車(chē)間內(nèi)部粉塵隨時(shí)間和空間運(yùn)移的規(guī)律,獲取通風(fēng)除塵優(yōu)化的參數(shù),以茫崖石棉礦第一選礦廠篩分車(chē)間為研究背景,依據(jù)氣固兩相流理論,采用計(jì)算機(jī)流體力學(xué)的離散相(DPM)模型對(duì)篩分車(chē)間粉塵濃度分布規(guī)律數(shù)值模擬,并與現(xiàn)場(chǎng)粉塵濃度實(shí)測(cè)數(shù)據(jù)比較分析,模擬結(jié)果和實(shí)測(cè)數(shù)據(jù)相吻合.研究結(jié)果表明:篩分設(shè)備附近粉塵濃度較高,以篩分設(shè)備為中心隨著距離增加粉塵濃度降低;捕集邊界下粉塵濃度比反彈邊界較低,粉塵捕集效果更好;篩分車(chē)間進(jìn)風(fēng)風(fēng)速控制在 0.6 m/s左右時(shí),粉塵沉降效果較好;安裝抽風(fēng)集塵罩后,主抽風(fēng)管風(fēng)速為 14 m/s時(shí),平均控塵效率達(dá)到90%,石棉纖維濃度控制在2.52 f/mL以下.
石棉篩分車(chē)間;粉塵濃度;運(yùn)移規(guī)律;離散相;數(shù)值模擬
石棉因其具有獨(dú)特的耐腐蝕性、隔熱性和強(qiáng)抗拉性等優(yōu)良特性,廣泛應(yīng)用于航天、船舶、消防、特殊制造等領(lǐng)域[1-2].國(guó)內(nèi)石棉礦產(chǎn)資源豐富,工業(yè)使用量較大,2014年使用量達(dá)到50萬(wàn)噸.近幾年歐美、德國(guó)、日本等國(guó)家禁止生產(chǎn)含石棉成分的產(chǎn)品;國(guó)內(nèi)采取全面禁止使用青石棉,安全使用溫石棉的方針[3].石棉在開(kāi)采、選礦、加工等過(guò)程容易產(chǎn)生粉塵,污染新鮮空氣,威脅作業(yè)人員的健康,特別是粉塵含有微細(xì)纖維,人體器官組織吸入后易附著和沉降,導(dǎo)致石棉肺、肺癌、間皮瘤等疾病[4-6].篩分作業(yè)作為選礦工藝中重要的工序,主要采用振動(dòng)篩分設(shè)備,通過(guò)網(wǎng)篩不停的振動(dòng),分離粒徑大于網(wǎng)篩孔徑的塊石,由于網(wǎng)篩循環(huán)的震蕩,致使礦石表面的粉塵揚(yáng)起,擴(kuò)散到車(chē)間污染空氣.目前,國(guó)內(nèi)外對(duì)粉塵控制研究主要采用理論分析、相似實(shí)驗(yàn)、數(shù)值模擬等方法研究粉塵濃度分布規(guī)律.國(guó)內(nèi)學(xué)者的研究主要集中在礦山作業(yè)面[7-8],在石棉篩分車(chē)間粉塵方面的研究較少.國(guó)外學(xué)者在工業(yè)粉塵控制做了一定的研究,例如Silvester等[9]針對(duì)壓碎破碎設(shè)備車(chē)間粉塵控制,通過(guò)計(jì)算流體動(dòng)力學(xué)軟件預(yù)測(cè)車(chē)間粉塵分布;Constance[10]分別對(duì)稀釋通風(fēng)和局部通風(fēng)兩種控塵措施的優(yōu)缺點(diǎn)進(jìn)行概述.本文針對(duì)石棉篩分車(chē)間建立幾何模型,通過(guò)數(shù)值模擬車(chē)間不同條件下粉塵的運(yùn)移規(guī)律,結(jié)合現(xiàn)場(chǎng)實(shí)測(cè)數(shù)據(jù),獲得篩分車(chē)間最優(yōu)通風(fēng)控塵參數(shù),指導(dǎo)現(xiàn)場(chǎng)控塵改造,對(duì)于保障作業(yè)人員身體健康有重要意義.
粉塵粒子在空氣運(yùn)移的理論基礎(chǔ)是氣固兩相流理論,目前,在數(shù)值計(jì)算方面主要分兩種方法:歐拉-歐拉方法和歐拉-拉格朗日方法.其中,歐拉-拉格朗日方法是運(yùn)用歐拉法、拉格朗日法分別處理背景、離散流體,將氣體作為背景流體,粉塵粒子視為離散流體,離散相模型(DPM)的理論基礎(chǔ)就是基于該方法.本文運(yùn)用離散相模型研究石棉選廠篩分車(chē)間粉塵運(yùn)動(dòng)規(guī)律,將車(chē)間內(nèi)部空氣視為背景流體,采用歐拉法進(jìn)行研究;將塵顆粒作為離散流體,采用拉格朗日法研究粉塵粒子運(yùn)移線路,最終得出粉塵在車(chē)間空氣中的濃度分布.
假定流體為不可壓縮的牛頓流體,忽略體積力,則連續(xù)相的運(yùn)動(dòng)方程選用三維不可壓縮Navier-Stokes方程:
連續(xù)方程:
(1)
動(dòng)量守恒方程:
(2)
式中:ρ為氣體密度,kg/m3;τij為應(yīng)力張量;p為流體相壓力,Pa;g為重力加速度,m/s2;xi,xj分別為x,y方向上的坐標(biāo),m;ui,uj分別為流體在x,y方向上的速度(m/s);Fi為控制體平均的顆粒流體阻力,N.
k-ε湍流動(dòng)能方程:
Gk-ρε+Sk
(3)
(4)
通過(guò)積分拉格朗日坐標(biāo)下顆粒作用力的微分方程來(lái)求解顆粒的軌跡,在求解過(guò)程中,只考慮阻力和重力及顆粒相的作用力[11-13].
(5)
式中:FD(u-up)為顆粒的單位質(zhì)量阻力;FC為顆粒與顆粒(邊界)碰撞力;FD可根據(jù)式(4)計(jì)算:
(6)
石棉選廠篩分車(chē)間主要有供料皮帶間、篩分設(shè)備間、物料分類(lèi)收集間3部分,幾何模型圖如圖1所示.設(shè)備間長(zhǎng)12 m、寬9 m、高4 m;車(chē)間安裝2臺(tái)篩分機(jī),篩分機(jī)尺寸為長(zhǎng)4 m、寬1 m、高1.2 m;開(kāi)有兩扇門(mén),高3 m、寬2 m;給料管段斷面為0.8 m×0.6 m.集塵罩整體形狀為規(guī)則的六面體,大罩口斷面1.0 m×0.6 m,集塵罩小口直接與抽風(fēng)通連接.采用Gambit軟件劃分模型網(wǎng)格,詳見(jiàn)圖2.
圖1 篩分車(chē)間幾何模型圖Fig.1 The geometrical model of screening workshop
圖2 篩分車(chē)間網(wǎng)格劃分Fig. 2 The meshing of screening workshop
根據(jù)茫崖石棉礦第一選廠篩分車(chē)間的具體情況和相關(guān)實(shí)測(cè)數(shù)據(jù),結(jié)合CFD相關(guān)理論,對(duì)FLUENT數(shù)值模擬進(jìn)行參數(shù)設(shè)定[14-16],詳見(jiàn)表1.
表1 計(jì)算模型參數(shù)設(shè)定表Tab.1 The calculation model parameters
設(shè)置車(chē)間進(jìn)風(fēng)口風(fēng)速為 0.25 m/s,通過(guò)對(duì)車(chē)間風(fēng)流流場(chǎng)進(jìn)行數(shù)值模擬,得到風(fēng)流場(chǎng)速度矢量圖和風(fēng)流速度云圖,如圖3,圖4所示.從圖中看出:①風(fēng)流進(jìn)入車(chē)間先沿著風(fēng)流初始方向向前運(yùn)動(dòng),隨后前方受到車(chē)間壁面邊界的阻擋后,風(fēng)向幾乎發(fā)生90°變化流向車(chē)間出口.②風(fēng)流流場(chǎng)影響區(qū)域呈現(xiàn)不斷擴(kuò)大的趨勢(shì),流場(chǎng)風(fēng)速則是呈現(xiàn)減小的趨勢(shì),風(fēng)流受附壁效應(yīng)的影響,流向車(chē)間中央風(fēng)流較少,形成漩渦區(qū),風(fēng)流交換周期較長(zhǎng).③根據(jù)風(fēng)流狀態(tài)不同分為:射流區(qū)、渦流區(qū)、回流區(qū)、出口區(qū),射流區(qū)和出口區(qū)風(fēng)速在0.20~0.25 m/s,回流區(qū)風(fēng)速保持在 0.10~0.20 m/s,渦流區(qū)風(fēng)速范圍 0~0.10 m/s.
圖3 篩分車(chē)間風(fēng)流場(chǎng)速度矢量分布圖Fig. 3 The distribution of velocity vector in screening workshop
圖4 篩分車(chē)間風(fēng)流速度云圖Fig. 4 The speed cloud in screening workshop
圖5 粉塵顆粒運(yùn)動(dòng)軌跡圖Fig. 5 The particle trajectory of dust particles
圖6 篩分車(chē)間粉塵濃度空間分布圖Fig. 6 The dust concentration distribution in screening workshop
為直觀觀察粉塵粒子在篩分車(chē)間內(nèi)的運(yùn)動(dòng)軌跡,在離散相模型設(shè)置篩分機(jī)物料出口處隨機(jī)產(chǎn)生120個(gè)粉塵粒子,運(yùn)用隨機(jī)游走模型(DRW)追蹤粒子運(yùn)動(dòng)軌跡,得到圖5.圖6,圖7分別為車(chē)間粉塵質(zhì)量濃度空間分布圖和分布云圖.從圖5~圖7得出:①粉塵從塵源產(chǎn)生后隨風(fēng)流運(yùn)動(dòng)方向進(jìn)行逸散,粉塵受到壁面邊界阻擋和碰撞后停止運(yùn)動(dòng).②在篩分設(shè)備物料出口產(chǎn)生的粉塵濃度達(dá)到最大值,隨著距離該區(qū)域距離增大粉塵濃度呈降低趨勢(shì).③粉塵受車(chē)間壁面邊界阻擋和碰撞等效應(yīng),同時(shí)部分粉塵隨風(fēng)流排出,在不同程度上起到降低粉塵的作用,但車(chē)間內(nèi)粉塵濃度依然較大,平均濃度約 65 mg/m3,篩分設(shè)備物料出口濃度高達(dá) 186.5 mg/m3,中央漩渦區(qū)濃度低于 28 mg/m3且粉塵停留時(shí)間較長(zhǎng),排塵與沉降效果差.
為比較不同邊界條件篩分車(chē)間粉塵運(yùn)動(dòng)和濃度分布規(guī)律的差異性,分別模擬了邊界條件設(shè)置為捕集和反彈兩種情況,圖7,圖8分別為篩分車(chē)間邊界設(shè)置為捕集條件、反彈條件粉塵濃度分布云圖.經(jīng)對(duì)比模擬結(jié)果發(fā)現(xiàn):在粉塵濃度分布特征上兩者基本一致,在數(shù)值上反彈邊界情況較大,由此可見(jiàn),在篩分車(chē)間日常作業(yè)過(guò)程中,現(xiàn)有工藝允許條件下,采取適當(dāng)?shù)貪?rùn)濕墻面、地板的措施,加強(qiáng)對(duì)壁面的捕集效率,有助于減輕篩分車(chē)間粉塵污染.
圖7 篩分車(chē)間粉塵濃度分布云圖Fig. 7 The dust concentration cloud in screening workshop
圖8 邊界設(shè)置反彈時(shí)粉塵濃度云圖Fig. 8 The dust concentration cloud under reflect wall condition
研究篩分車(chē)間不同進(jìn)風(fēng)風(fēng)速條件粉塵濃度空間分布情況,選取了車(chē)間進(jìn)風(fēng)風(fēng)速為0.20 m/s,0.40 m/s,0.60 m/s,0.80 m/s 4種情況下,換算成進(jìn)風(fēng)風(fēng)量分別對(duì)應(yīng)為1.2 m3/s,2.4 m3/s,3.6 m3/s,4.8 m3/s,分別進(jìn)行模擬,模擬結(jié)果詳見(jiàn)圖9.為了量化不同進(jìn)風(fēng)風(fēng)速排塵效果,對(duì)車(chē)間內(nèi)人體呼吸帶高度(H=1.5 m)平面粉塵濃度取平均值,進(jìn)風(fēng)風(fēng)速為0.20 m/s,0.40 m/s,0.60 m/s,0.80 m/s 4種情況下對(duì)應(yīng)的呼吸帶高度粉塵濃度平均值分別為97.58 mg/m3,82.42 mg/m3,70.87 mg/m3,67.21 mg/m3.從模擬結(jié)果看出:當(dāng)進(jìn)風(fēng)風(fēng)速在 0.20~0.80 m/s區(qū)間,篩分車(chē)間排塵效果隨著風(fēng)速變大而增強(qiáng);當(dāng)進(jìn)風(fēng)風(fēng)速?gòu)?.60 m/s增加到0.80 m/s時(shí),排塵效果增幅較小.考慮到當(dāng)風(fēng)速較大時(shí),風(fēng)流流動(dòng)容易揚(yáng)起車(chē)間地面積塵,產(chǎn)生二次揚(yáng)塵;當(dāng)風(fēng)速較小時(shí),車(chē)間內(nèi)部排塵效果不好.因此,綜合考慮,建議篩分車(chē)間進(jìn)風(fēng)風(fēng)速控制在0.6 m/s左右.
圖9 不同進(jìn)風(fēng)風(fēng)速下粉塵濃度分布云圖Fig. 9 The dust concentration cloud at different inlet wind speeds
為改善車(chē)間作業(yè)環(huán)境,在兩臺(tái)篩分設(shè)備的物料出口處安裝集塵罩,用直徑為400 mm的風(fēng)管與集塵罩連通,模擬主抽風(fēng)管風(fēng)速為10 m/s,12 m/s,14 m/s,16 m/s 4種情況車(chē)間粉塵濃度分布,車(chē)間進(jìn)風(fēng)風(fēng)速為0.6 m/s,控塵效果如圖10所示.對(duì)比分析得出:安裝抽風(fēng)集塵罩后,大部分粉塵經(jīng)集塵罩和抽風(fēng)管排出,車(chē)間內(nèi)部粉塵濃度下降明顯,粉塵污染得到良好的控制.隨著主抽風(fēng)管風(fēng)速增加,控塵效果先顯著增強(qiáng),后趨于穩(wěn)定,當(dāng)抽風(fēng)風(fēng)速達(dá)到14 m/s時(shí),抽風(fēng)集塵罩基本能控制篩分設(shè)備物料出口處粉塵的外逸,控塵效果較好,當(dāng)增加抽風(fēng)風(fēng)速至16 m/s時(shí),控塵效果趨于穩(wěn)定.綜合篩分車(chē)間控塵效果和風(fēng)機(jī)耗能等因素,最終確定抽風(fēng)集成罩主抽風(fēng)管適宜風(fēng)速為14 m/s.
圖10 不同抽風(fēng)風(fēng)速篩分車(chē)間控塵效果圖Fig. 10 The dust removal effect at different extraction wind speeds
依據(jù)GBZ/T192.1—2007,GBZ/T192.5—2007以及相關(guān)文獻(xiàn)[17-18],結(jié)合篩分車(chē)間空間結(jié)構(gòu)和產(chǎn)塵源位置情況,對(duì)車(chē)間內(nèi)呼吸帶高度布置10個(gè)測(cè)點(diǎn),測(cè)點(diǎn)布置如圖11所示.現(xiàn)場(chǎng)采用IFC-2防爆型粉塵采樣儀,選用過(guò)氯乙烯纖維濾膜(孔徑0.8 μm)分別對(duì)集塵罩安裝前后粉塵進(jìn)行采樣.實(shí)驗(yàn)室使用BK5000相差顯微鏡對(duì)樣本石棉纖維濃度進(jìn)行測(cè)定,數(shù)據(jù)結(jié)果如表2所示,采樣濾膜處理后在顯微鏡下觀察石棉纖維形態(tài),如圖12所示.運(yùn)用濾膜稱(chēng)重法對(duì)樣本進(jìn)行粉塵濃度測(cè)定,每個(gè)測(cè)點(diǎn)采用3次以上重復(fù)操作取平均值,并將實(shí)測(cè)數(shù)據(jù)與模擬結(jié)果進(jìn)行對(duì)比,對(duì)集塵罩安裝前后的控塵效率進(jìn)行計(jì)算,如圖13所示.
圖11 粉塵測(cè)點(diǎn)布置圖Fig. 11 The layout of dust measuring points
測(cè)定數(shù)據(jù)測(cè)點(diǎn)編號(hào)12345678910集塵罩安裝前石棉纖維濃度/(f·mL-1)23.2120.8314.1612.4417.6019.826.229.864.113.26集塵罩安裝后石棉纖維濃度/(f·mL-1)2.522.341.551.421.862.100.961.110.640.58
圖12 采樣濾膜石棉纖維在顯微鏡下放大視野圖Fig.12 The pictures of asbestos fibers on the sampling membrane under microscope
圖13 抽風(fēng)集塵罩安裝前后粉塵濃度實(shí)測(cè)與模擬數(shù)據(jù)Fig.13 The measured and simulated data of dust concentration before and after installation of collector
如圖12為石棉纖維在顯微鏡下放大的視野圖,石棉纖維的形態(tài)呈現(xiàn)細(xì)條針絲狀,而巖塵顆粒為細(xì)小顆粒狀,石棉粉塵中還有微細(xì)纖維,人體吸入體內(nèi)后,容易附著于器官組織引起病變.由表2,圖13可以看出:①篩分車(chē)間安裝集塵罩前后模擬結(jié)果和實(shí)測(cè)數(shù)據(jù)基本吻合,說(shuō)明幾何建模和離散相模型(DPM)等相關(guān)的設(shè)置均合理,數(shù)值模擬結(jié)果具有一定的可靠性.②經(jīng)過(guò)對(duì)比集塵罩安裝前后的各測(cè)點(diǎn)粉塵濃度數(shù)據(jù),發(fā)現(xiàn)安裝集塵罩后,粉塵通過(guò)風(fēng)管抽走,篩分車(chē)間內(nèi)部粉塵急劇下降,各測(cè)點(diǎn)的平均控塵效率達(dá)到90%.③集塵罩安裝后,篩分車(chē)間粉塵濃度降低的同時(shí),粉塵中石棉纖維濃度也得到了良好的控制,1號(hào)測(cè)點(diǎn)石棉纖維濃度由原來(lái)最高的23.21 f/mL下降至2.52 f/mL.圖14為抽風(fēng)集塵罩安裝前后篩分車(chē)間的現(xiàn)場(chǎng)照片.
(a)安裝前 (b)安裝后圖14 抽風(fēng)集塵罩安裝前后車(chē)間作業(yè)時(shí)現(xiàn)場(chǎng)照片F(xiàn)ig. 14 The workshop photos before and after the installation of the exhaust dust collector
通過(guò)對(duì)茫崖石棉礦第一選礦廠篩分車(chē)間粉塵濃度分布進(jìn)行數(shù)值模擬,并與現(xiàn)場(chǎng)實(shí)測(cè)粉塵濃度比較分析,得到如下結(jié)論與建議:
1)兩臺(tái)篩分設(shè)備附近粉塵濃度較大,并以篩分設(shè)備為中心隨著距離增大粉塵濃度呈現(xiàn)降低的趨勢(shì).建議對(duì)篩分設(shè)備采取防塵降塵措施,從塵源位置遏止粉塵逸散.
2)與反彈邊界相比,捕集邊界下車(chē)間內(nèi)粉塵濃度更低,捕集粉塵顆粒效果更好.在工藝允許前提下,適當(dāng)采取地濕潤(rùn)車(chē)間墻壁、地面、頂板等措施.
3)根據(jù)車(chē)間進(jìn)風(fēng)口和出風(fēng)口的現(xiàn)有布局情況,通過(guò)數(shù)值模擬得出:當(dāng)車(chē)間進(jìn)風(fēng)風(fēng)速控制在0.6 m/s左右時(shí),能夠較好地排塵車(chē)間粉塵.建議將篩分車(chē)間進(jìn)風(fēng)風(fēng)速設(shè)為 0.6 m/s左右.
4)在兩臺(tái)篩分設(shè)備物料出口處安裝負(fù)壓抽風(fēng)集塵罩后,各測(cè)點(diǎn)的平均控塵效率達(dá)到90%,車(chē)間石棉纖維濃度控制在 2.52 f/mL以下,主抽風(fēng)管風(fēng)速建議控制在 14 m/s時(shí)為宜.
抽風(fēng)控塵研究的內(nèi)容還有很多,其中集塵罩的尺寸、形狀、布置方式等均可做進(jìn)一步深入的研究.
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Numerical Simulation of Dust Mass Concentration Distribution inScreening Workshop of Asbestos Concentrator
JIANG Zhongan1?,DENG Quanlong1,SHI Xunxian2,CHEN Jushi1
(1.Key Laboratory of Minitry of Education for Efficient Mining and Safety of Metal Mine,University ofScience and Technology Beijing,Beijing 100083,China;2.Institute of Industrial Safety,China Academy of Safety Science & Technology,Beijing 100012,China)
In order to master the regularities of dust movement with time and space in the screening workshop of asbestos concentrator and obtain the optimized parameters of dust removal by ventilation,screening workshop of No. 1 concentrator in Mangya Asbestos Mine was considered as the research background. Based on the theory of gas-solid two-phase flow,the discrete phase model (DPM) of computational fluid mechanics was used to simulate the dust concentration in screening workshop. By comparing with field measurement of dust concentration distribution,simulation results are essentially coincident with the measured data. The results indicate that the dust concentration near the screening equipment is higher,and the value decreases as the distance from the screening equipment increases. The dust concentration is lower under trap wall condition than the reflect,and the dust trapping effect is better. The dust settling effect is better when the inlet wind speed is about 0.6 m/s. When the exhaust dust cover is installed and the wind speed of main exhaust pipes is maintained at 14 m/s,the average dust-removal efficiency can reach 90%,and the asbestos fiber concentration can be controlled below 2.52 f/mL.
asbestos screening workshop; dust concentration; migration regularity; discrete phase; numerical simulation
1674-2974(2017)12-0135-07
10.16339/j.cnki.hdxbzkb.2017.12.021
2017-02-07
國(guó)家科技支撐計(jì)劃資助項(xiàng)目(2015BAK40B02),National Science and Technology Support Program(2015BAK40B02);國(guó)家自然科學(xué)基金資助項(xiàng)目(51574016),National Natural Science Foundation of China(51574016);北京市自然科學(xué)基金青年科學(xué)基金資助項(xiàng)目(8164010),the Young Scientists Fund of the Beijing Municipal Natural Science Foundation(8164010);中央高?;究蒲袠I(yè)務(wù)費(fèi)專(zhuān)項(xiàng)資金資助項(xiàng)目(FRF-BD-17-007A),Fundamental Research Funds for the Central Universities(FRF-BD-17-007A)
蔣仲安(1963-),男,浙江諸暨人,北京科技大學(xué)教授,博士?通訊聯(lián)系人,E-mail: jza1963@263.net
X964
A